Department of Mechanical and Mechatronic Engineering

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Data-driven regression models for voyage cost optimisation based on the operating conditions of the SA Agulhas II
(Stellenbosch : Stellenbosch University, 2020-12) Durandt, Petrus Gerhardus; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: The maritime industry is a cornerstone in the modern globalised economy. Efficient operation of ocean-going vessels is of great importance from both financial and environmental perspectives. Carbon emissions from maritime activities are projected to increase significantly in the coming decades. Short term strategies to address the carbon footprint issue calls for research around topics such as efficiency optimisation of ocean-going vessels.Emerging digital twin platforms are allowing asset owners and operators to manage the vast information networks that monitor asset performance. Dig-ital twins provide a way to plan, monitor and simulate various operating environments to find optimum configurations. Machine learning methods are harnessed to provide an innovative solution to modelling of data-driven problems which could be very useful in the prediction of asset responses for various operational scenarios. Speed and route optimisation with the use of data-driven models are prerequisites in the attempt to provide decision support capacity to gain tactical foresight for maritime operations. The SA Agulhas II (SAAII) is a polar supply and research vessel owned and operated by the South African Department of Environment, Forestry and Fisheries (DEFF). This vessel is of particular importance due to the large quantity and variety of data, for both open water and ice navigation, that are recorded during annual voyages to Antarctica, Marion and Gough Islands. Data is comprised of physical measurements from on-board sensors and diligent observations of ocean and ice conditions. Reconciliation and synchronisation of observed and machine data from the ship’s central measurement unit (CMU)was successful and paved the way towards effective data-driven modelling.Two different machine learning models, support vector regression (SVR) and artificial neural networks (ANN), were trained to predict the powering performance of the SAAII for open water and ice navigation while subjected to various atmospheric and ocean conditions. Output power is directly relatable to fuel consumption and was successfully estimated from trained models. Anon-linear relationship between power and speed is observed and provides an opportunity to optimise ship operations in terms of cost or time.Speed optimisation illustrates the financial cost-benefit impact of operating at higher speeds and power levels. A pilot exercise is defined to assess the applicability of data-driven models in a route selection context. A dynamic optimisation technique is successfully implemented to account for the stochastic, time-series characteristics of weather conditions over a voyage path. Data-driven modelling and optimisation offer breakthrough opportunities to ensure the modernisation and sustainability of the SAAII in the context of a South African presence within Antarctic and Southern Ocean research.
The detection and analysis of wave slamming from full-scale ship measurements.
(Stellenbosch : Stellenbosch University, 2018-12) Saunders, Clinton Frederick Wood; Bekker, Annie; Muiyser, Jacques; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Bow and stern wave slamming has proven to be a persisting and concerning problem on the S.A. Agulhas II. Various full-scale vibration measurements have been conducted over several voyages in the Southern Ocean. Past research has concluded that vibration has reached levels where damage was possible in the stern and is probable in the bow during open water navigation (Soal, 2014). In order to better understand the drivers behind slamming, an algorithm was developed to detect and count slamming events in full-scale signals. Detection was done in the time domain using acceleration peaks, as well as the frequency domain using a wavelet transform. Statistical thresholds were then determined using a median absolute deviation. The data in the frequency domain provedmost accurate for counting slams. Slamming counts were then compared with environmental and operational variables for the voyages. It was determined that these variables have a significant effect on the frequency of slamming events.
The detection and quantification of wave slamming from full-scale measurements on a polar vessel
(Stellenbosch : Stellenbosch University, 2020-12) Bossau, J. C.; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: The SA Agulhas II is a polar supply and research vessel. Her extended transom design predisposes her to stern slamming, which may lead to significant high transient whipping responses. Slamming is a concern for the fatigue life of the vessel and may lead to local damage. Slamming and whipping are investigated through full-scale measurements of ship responses, recorded concurrently with the associated vessel operational parameters and environmental conditions encountered during purposely executed open water manoeuvres. A systematic operational study was conducted accordingly, whereby the relative heading and vessel speed were regulated in consistent wave states. Firstly, slamming events need to be accurately detected from signals measured with an accelerometer array in the vessel hull. The MATLAB findpeaks function, the continuous Morlet wavelet transform and a spectrogram method were implemented. The continuous Morlet wavelet transform and findpeaks method showed the most promising slamming detection capabilities. It was determined that the proposed slamming detection methods require a threshold to identify structurally significant slams and reject slams of smaller magnitude. The peak acceleration amplitude at the time of impact is extracted and the impact site is determined. Typically, more slams are detected at the stern and the peak magnitude of the acceleration measurements is also greatest at the stern. A structural vibration analysis reveals that high velocity levels are potentially a concern for fatigue and may lead to structural damage. Operational modal analysis techniques determined the hull flexure vertical bending response magnitude resulting from wave-induced vibration. The frequency of stern slams is shown to be highest when the vessel is held on station in following and stern-quartering seas and the corresponding acceleration magnitude is largest at the stern under these conditions. It is shown that stern slamming gives rise to higher vibration velocity levels, which indicate that damage is probable for conditions associated with prevalent stern slams of larger magnitude. The frequency and magnitude of slamming incidence detected at the stern can similarly be shown to concur with the associated flexural response, as the first bending mode dominates the response when the ship encounters following and stern-quartering waves during stationary or low-speed operations. The slamming and associated vertical bending mode whipping response is reduced under these conditions as the wave encounter frequency is decreased with increasing vessel speed. Conversely, as the speed increases, more slamming and a greater bending response is observed for head and bow-quartering seas. Consequently, results indicate potential structural damage attributed to stern slamming and whipping, which is exacerbated in following seas when the vessel is stationary. The quantification of wave slamming presented in this thesis therefore warrants a further investigation into the contribution of whipping to fatigue damage in conjunction with a conventional fatigue analysis.
The development of a service oriented architecture for digital services on maritime vessels
(Stellenbosch : Stellenbosch University, 2022-04) Bunn, Nicholas Raymond; Kruger, K.; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH SUMMARY: Digitalisation efforts in the maritime domain have, until now, predominantly focussed on ports and terminals. Contributions to the adoption of digitalisation technologies on vessels themselves stem mostly from industry, although the value of doing so has become increasingly apparent where digitalisation is said to present opportunities for improved vessel operation and performance. A popular approach to digitalisation, identified in the manufacturing and Industry 4.0 realms, is that of service-orientation and digital services. Here, systems are composed of discrete contributions, providing flexible and adaptable solutions to digitalisation challenges in dynamic environments with evolving needs. This thesis details the design, development, and evaluation of a service-oriented architecture to aid in decision-making on maritime vessels. This architecture takes a microservice approach to service-orientation, employing a custom variation of the API-gateway pattern to enable a flexible and reconfigurable system. The proposed architecture includes an aggregation layer to abstract coordination activities from the service layer, negating the need for a service-mesh in the backend. The architecture is tested and evaluated through a case study, carried out on the icebreaking polar supply and research vessel, the S.A. Agulhas II. This case study deploys information services and existing engineering models describing the vessel as microservices. Aggregating services are designed to leverage these services, providing information to aid in route planning and support more informed decision-making. The case study details specific technology implementations to provide the specified platform functionality, with the most notable of these being gRPC as an RPC framework. The experiments indicate that RPC is a suitable communication mechanism for in-memory aggregation and real-time data delivery in this context. However, it was discovered that the gRPC interceptor functionality is not a robust choice for all cases of rate-limiting and retry logic, and recommendations are provided for a revision of these components. This thesis concludes that the proposed architecture is successful in providing a reconfigurable service-oriented architecture for digital service delivery on maritime vessels. Generic platform components were developed in the four programming languages used in the case study, showcasing the interoperability of services written in various languages, and by various domain experts, within the system.
Experimental investigation of a gimbal in the frequency domain
(2019-04) Haller, Michen Christian; Smit, Willie; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering (CRSES)
ENGLISH ABSTRACT: When it comes to renewable energies, the reduction of initial investment costs help make these generation methods a more viable option for governments, or private companies. For Concentrated Solar Power (CSP) plants, a particular example of this would be the initial investment costs associated with the heliostats. Heliostat foundation preparation and heliostat structure quality need to be of a high standard for a heliostat to remain within its calibration parameters for long periods of time. If calibrations, inspections and cleaning of these heliostats can be done more regularly, the time for which the heliostat needs to maintain its calibration parameters is reduced, thereby reducing foundation preparation costs and heliostat manufacturing costs. At the University of Stellenbosch, the Solar Thermal Energy Research Group (STERG) is investigating the use of automated drones to perform inspections, calibrations and cleaning of heliostats. In order to attach sensors to the drone, a gimbal is used. This isolates the sensor from the drone’s rotations. Gimbal dynamic performance data, which is relevant to design engineers, is not readily available. In this thesis, the pitch responses of a two-axis gimbal to pitch and roll disturbances are measured for varying disturbance frequencies and amplitudes, without vibration isolation pads. In addition to producing the gimbal performance data, it is found that the largest gains observed occurred in region where no structural natural frequencies were found. It is suspected that the knocking of the gimbal Inertial Measurement Unit (IMU) cable, which is connected to the device-mount IMU, is the source of these peak responses. The responses to pitch and roll actuations differed significantly, with the largest reponse attenuation observed for pitch actuations between 31 Hz and 46 Hz. It is also found that the gimbal is sensitive to frame vibrations, especially at frame natural frequencies, which highlights the need for vibration isolation pads during use. It is recommended that further research be conducted in the frequency domain for roll and yaw responses. In addition, it is recommended that the efficacy of gimbal vibration isolation pads, for blade pass frequencies, be investigated. Lastly, it is recommended that a more detailed analysis of the gain attenuation observed for the responses to pitch actuations, be conducted.
Full-scale measurement and quantification of hull fatigue on a slamming-prone polar vessel
(Stellenbosch : Stellenbosch University, 2022-04) Pferdekämper, Karl-Heinz; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH SUMMARY: The safe extension of existing asset life and operation of new record-sized ships require an improved understanding of ship fatigue. Both low-frequency wave bending and high-frequency flexural vibration fatigue hull structures. The former is caused by the weight distribution of the vessel and the location of support provided by dynamic wave crests. Whipping and springing contribute to high-frequency fatigue and occur when waves excite the flexural bending modes of the ship girder. Full-scale measurement campaigns have found that flexural vibration comprises up to 57% of the total fatigue in container ships. However, the adequate consideration of this component has not been consistently formalised in design codes. The addition of midship strain sensors to an existing full-scale measurement array onboard the SA Agulhas II enables the study of fatigue from vertical wave bending moments and flexural bending modes. This instrumentation realises an opportunity to study fatigue on a vessel with ice-capable hull features that make her prone to slamming during open-water operation. Subsequently, fatigue damage computed us- ing Miner's law and rainflow cycle counting shows significant high-frequency fatigue contributions during a storm case and a sequence of dedicated tests. During these systematic tests, 46 times more damage was accrued for the stationary vessel in fol- lowing waves than the equivalent test in head seas, with the increase dominated by high-frequency bending. Considerable stern slamming was noted for the stationary vessel in following waves. A slamming detection algorithm identified a correlation between slamming frequency and magnitude, and increased high-frequency fatigue. Furthermore, operational modal analysis confirmed that the first vertical bending mode dominates the flexural response with respect to energy and fatigue contribu- tion. Despite cracking near the measurement location, the accrued damage for the selected study detail does not exceed allowable design levels for a 30-year service life. However, significant fatigue from flexural vibration due to slamming is of concern for poorly designed detail and larger ships with higher stress amplitudes. In addition, current long-term structural analysis procedures considering only wave bending are reviewed. A new technique considering common routings and direc- tional sea state statistics, developed for remote regions of the Southern Ocean using open-source reanalysis data, is proposed. This spectral fatigue analysis is supported by vertical bending load response amplitude operators computed using commercial software. Results indicate that routes with a Westerly heading component accrue up to 14 times more damage than their Easterly return due to increased time en- countering head seas. For the SA Agulhas II, the annual voyage from Cape Town to Antarctica accrues the most damage as it crosses two high damage rate zones. Low-frequency wave bending fatigue computed from full-scale measurements com- pare well with spectral results for incremental speed tests into head seas. The dis- crepancies noted for stationary tests require further investigation. It is recommended that the strain measurement point be altered to remove local bending effects. Fur- thermore, finite element analysis and non-linear hydrodynamic simulations stand to further the study of flexural fatigue.
The impact of wave slamming indused vibration on human factors and equipment on board the SA Agulhas II
(Stellenbosch : Stellenbosch University, 2016-03) Omer, Hamza; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: An investigation of wave slamming phenomenon was performed in the context of human factors on-board the S.A. Agulhas II, a South African Polar Supply and Research Vessel. Full scale vibration measurements were conducted during the vessel’s voyage to Marion Island in 2014 and Antarctica in 2014/15. The measurements captured vibrations in the vertical direction as per the directives of ISO 2631-1 (1997). A questionnaire survey was conducted on both voyages to acquire the human response to wave slamming. The study for the Marion Island voyage focused on measurement and analysis of vibration due to slamming using the metrics recommended by ISO 2631-1 (1997). The analysis revealed that slamming events produce impulsive accelerations of high magnitude resulting in broad band excitation of the vessel. The weighted r.m.s acceleration levels resulting from slamming exceeded the comfort threshold provided by the standard. The qualitative analysis of human response indicated that slamming not only caused discomfort on-board but also affected work and equipment. The study performed during the Antarctic voyage was designed to identify and correlate measured slamming vibration data with human response and to investigate their association. Statistical analysis, performed using Kendall’s coefficient, indicated that slamming vibration was correlated to human complaints on-board the S.A. Agulhas II. The highest correlation found was the cumulative Vibration Dose Values (VDV) which proved to be the best metric amongst all others to represent slamming vibration for human factors. In addition to that, the study evaluated the effects of some environmental factors such as swell height and wind speed on wave slamming. It was concluded that even moderate sea states can lead to heavy incidences of slamming. Finally, operational deflection shapes were calculated for the visualization of the structural response of the vessel during bow and a stern slamming event. Time domain response and frequency response was calculated to observe the motion of the ship as it undergoes a slamming event. The analysis indicated that the area of impact (bow or stern) comes under severe loading immediately. Both slamming events produce bending and twisting of the entire structure. It was also noted that the long duration of heavy oscillations produced by slamming may affect human comfort and performance on-board the vessel.
Inverse models for ice-induced propeller moments on a polar vessel.
(Stellenbosch : Stellenbosch University, 2021-03) Nickerson, Brendon Mark; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: It is necessary to quantify the loads experienced by the propellers of ice-going vessels.Knowledge of these loads will serve to improve propulsion design specifications and maintenance strategies for polar class ships. Recent developments include the inverse solutions of the external ice-induced propeller moments from indirect measurements on the propulsion shaft. These inverse solutions are performed using models that account for the dynamic influence of the shaft. Although torsional vibration calculations are required by design rules there is little information on the methodology external propeller moments as their use, in this context, is still relatively new. Full-scale propulsion shaft measurements were conducted on board the S.A. Agulhas II, in which the torque and angular velocity were captured, to be trans-formed into external propeller moments. Two inverse models of the propulsion shaft were investigated. The first is an existing model which represents the shaft as a combination of lumped masses. The inverse problem in this case is ill-posed and requires regularization. It was found that the assumptions made in the derivation of this model, that both the hydrodynamic and motor torques were constant, and its computational expense made it ill-suited for use in the inverse estimation of propeller moments. The second inverse model is newly developed and based on the superposition of the shaft modes, resulting in a well-posed problem. This model accounts for the modal inertia in the flexible modes of the shaft, as full-scale data indicated that this was important, and has increased accuracy and efficiency. To the author’s knowledge, this is the first model that has been efficiently applied to determine the inverse propeller moments from full-scale measurements for a complete voyage. The derivation of the corresponding estimated propeller load profiles is presented. The new model is suitable for the real-time monitoring of propeller loads, which can assist in ship operation.
An investigation of shaft line torsional vibration during ice impacts on PSRV's
(Stellenbosch : Stellenbosch University, 2017-03) De Waal, R. J. O.; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: In order to estimate the forces exerted on ship propellers during ice navigation, the rotational dynamics of the propulsion system need to be accurately modelled. The direct measurements of propeller loads of ships during ice navigation is challenged by the harsh operating environment. Indirect measurements are therefore performed on the shaft line of such ships to estimate propeller loads through an inverse problem. Three case studies are presented, namely open water, cavitation and ice navigation. The maximum torque loading on the shaft occurred during ice navigation and the maximum thrust case during cavitation. Ice-induced moments on the SAA II propeller were determined from shaft line measurements using inverse methods, whereby the maximum ice load was found to be 941 kNm. Estimated load profiles for navigation in the Arctic and Antarctica are presented using rainflow counting techniques. The aim of the present research was to perform data-driven modelling of the rotational dynamics of the shaft line to aid future design of ice going vessels.
An investigation of the seakeeping behaviour of a polar vessel in waves
(Stellenbosch : Stellenbosch University, 2021-03) Van Zuydam, Armand; Bekker, Annie; Meyer, C. J.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: The SA Agulhas II plays a crucial role in logistical and research support in the Southern Ocean and Antarctica. It is estimated that open water transits account for up to 85 % of her total voyages. She is built to Polar Class PC5 with a thick rounded stem and a full fore-body. Instinctively, these characteristics improve her performance in ice but may lead to sharp increases in open-water resistance and a ect other seakeeping aspects. In particular, her spoon-shaped bow and at raised transom predispose her to slamming. In rough sea conditions, signi cant motions are induced, which subsequently leads to an increase in resistance and fuel consumption. To ensure e cient performance at sea, vessel owners must have knowledge about a ship's responses in these environments. Therefore, an investigation was undertaken to evaluate the seakeeping behaviour of the SA Agulhas II. Full-scale measurements were conducted onboard the vessel during a cruise in the Southern Ocean. Data obtained from this campaign were used to determine the heave, roll and pitch motion responses in irregular waves. Strip theory was implemented to determine the motion Response Amplitude Operators of the vessel. Through superposition of the Response Amplitude Operators and the wave spectrum, the motion responses in irregular waves were predicted. A comparison between measured and predicted motion responses showed that heave and pitch could be predicted with reasonable accuracy. Roll motion showed various discrepancies and future research is recommended to study non-linear e ects, such as roll damping. Computational Fluid Dynamics was identi ed as an essential tool to investigate her motion responses and added resistance in head waves. During this work, three speeds were evaluated, her design speed of 14 kn, a reduced speed of 10 kn, and an increased speed of 18 kn. Overall, the results showed that the maximum heave and pitch motions are expected to occur when the encounter frequency ranges between 0.124-0.143 Hz. For all three speeds, the maximum added resistance in waves was observed when large-amplitude motion occurs. It was further shown that a reduction of speed from 14 kn to 10 kn could decrease her e ective power by 42 %. On the other hand, increasing speed by 4 kn from 14 kn to 18 kn could lead to a maximum increase in e ective power of 87 %. Computational Fluid Dynamics investigations further showed that slamming could occur at the bow region of the SA Agulhas II even though she is not operating in extreme conditions. Computational Fluid Dynamics shows clear potential for further investigations into bow and stern slamming for the SA Agulhas II.
Motion sickness and rigid body motion of a polar supply and research vessel on voyages to Antarctica and the Southern Ocean
(Stellenbosch : Stellenbosch University, 2016-03) Boulle, Brendan Guy; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Low frequency (0.1 Hz to 0.5 Hz) lateral and vertical motion present on ocean going vessels could cause motion sickness. ISO 2361-1 developed a means to predict motion sickness in the vertical direction, but did not propose a means on incorporating lateral motion. It was also hypothesised that motion on the SA Agulhas II is expected to be either more or less provocative depending on location. A modified six accelerometer array was developed in order to determine the lateral and vertical acceleration levels at any location on board the SA Agulhas II. Vertical acceleration was found vary along the width and length of the SA Agulhas II but was independent of height. Subjective responses of participants were collected from the personal details submission form and daily diary. It was reported that susceptibility towards motion sickness declined with age for the males. Females were found to be more susceptible than males. The percentage of motion sick participants, the percentage of vomiting participants and illness rating (N = 32) were correlated using Kendall's rank correlation. The percentage of motion sick participants and illness rating had the highest correlation coefficient (T) of 0.815. Participants spent most their time in the accommodation area, centred around zone D7. Daily maximum 6 h motion sickness dose values were determined at all locations on board the SA Agulhas II using vertical and lateral weighting filters for motion sickness. Illness rating correlated the best with both MSDVx;6h and MSDVz;6h. Linear and multiple non-linear regression analysis was used to determine the effects each direction, at zone D7, has on motion sickness. Motion in y-axis was determined to be insignificant. However multicollinearity was identified between x- and z-axis motion, which made determining the effects of each direction impossible. The contribution of each axis was then assumed to be the same and a linear regression model was developed to predict illness rating (R2 = 0:417).
Operational modal analysis on the SA Agulhas II
(Stellenbosch : Stellenbosch University., 2020-03) Van Zijl, Christof Moolman; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Full-scale operational measurements were conducted on a polar vessel during an expedition to Antarctica. Accelerometers distributed along the length of the vessel were used to capture vertical, lateral and torsional hull global motions. A parametric study on a stochastic subspace identification technique was conducted to investigate the effect of user-specified parameters on modal parameters. With low block sizes weakly excited modes were not identified and increasing block size up to fifty was found to reduce both random and bias errors. Measurement duration below twenty minutes were found to produce relatively large bias and random errors, however there was little improvement with increasing measurement duration beyond twenty minutes. Extreme model orders were found to produce scatter on estimates and a suitable range of model orders were found to be between 200 and 300. A modal model consisting of five modes was identified for the SA Agulhas II. Modes were automatically tracked across four different cases of operational data. Vertical bending modes were tracked consistently across all four cases, but lateral and torsional modes were not. Energy in modal responses were highest for vertical bending modes and significant energy was found to be concentrated around vertical bending modes during an open water storm case. An analysis of the time-varying behaviour of modes in the four cases revealed highly non-stationary modal responses during an open water storm and two ice cases. The transients were found to correspond with impulsive wave slamming events in open water and ship-ice interactions during ice breaking.
The psychoacoustics of electric vehicle signature sound
(Stellenbosch : Stellenbosch University, 2018-03) Swart, Daniel Johannes; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: The automotive industry is currently exploring the global sound sphere to identify a pleasant, safe and unique electric vehicle signature sound. Drive-train acoustics contribute to the performance benchmark of vehicles in the marketplace. Electric vehicle sound signatures differ vastly from those of internal combustion engines. Questions arise as to how these signature sounds relate to consumer experiences, and how the positive attributes of these sounds can be extracted and enhanced. The presented work aimed to investigate the objectively and subjectively evaluated attributes of electric vehicle signature sound, and the associated consumer satisfaction. A subjective evaluation procedure for the classification of the noise produced by electric vehicles was adapted from existing methodologies for internal combustions engines. Itwas found that ‘Calm’, ‘Deep’, ‘Rumbling’,‘Creative’ and ‘Futuristic’ semantics should be added to existing tests to typically describe electric vehicle sound character. The sound signatures of six standard production electric vehicles and one hybrid electric vehicle were benchmarked through constant speed andWide Open Throttle drives. Time and frequency domain analyses were used to compare the different vehicles, and results revealed that electric vehicles contain substantial sound energy in the upper frequency bands due to the tonal components. Lower sound pressure levels were achieved in a multi-stage gearbox, with regards to the high frequency content associated with electric motors. High Prominence Ratio levels, in excess of 10 dB,were found for electric vehicles and current literature points to diminished consumer satisfaction as a result. Furthermore, standard production electric vehicle sound signatures were evaluated against enhanced sound stimuli, based on subjective semantics and objective metrics, to determine the dimensions of electric vehicle sound quality that can lead to improved consumer satisfaction. The methodologywas to undertake two independent subjective evaluations, performed by a jury of 32 and 52 members respectively, to determine the perceived electric vehicle sound experience. Results showed that Sharpness is fundamental to governing the electric vehicle sound experience. Secondly, the underlying dimensions of electric vehicle sound quality are sparsely described in literature and was therefore investigated. A factor analysis found that additional to the dimensions of refinement and powerfulness of internal combustion vehicle sound, electric vehicles also have a third dimension associated with a ‘Futuristic’ factor. Lastly, a consumer satisfaction model was proposed through multiple linear regression and the 95th percentile Sharpness value. The model yielded promising results for both interior and motorbay sound signatures and is proposed as a means of gauging consumer satisfaction for electric vehicle sound quality. The complexity of electric vehicle sound character was discussed and recommendations were offered with respect to the design considerations of future electric vehicle sound signatures. A holistic approach regarding both subjective and objective evaluation methods is recommended for future electric vehicle research, in order to fully understand the attributes that govern electric vehicle sound quality.
System identification and modal tracking on ship structures
(Stellenbosch : Stellenbosch University, 2018-03) Soal, Keith Ian; Bekker, Annie; Bienert, J.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH SUMMARY: are currently based mainly on dynamic response feedback. Navigators decide on how to operate the vessel based on how they feel it pitching, heaving, rolling and vibrating. The aim of this thesis is to investigate the idea of using system identification and modal tracking on polar vessels towards the development of a decision aiding system. System identification provides a powerful tool for building mathematical models of dynamic systems. An open source toolbox (openSID) for system identification using Stochastic Subspace Identification (SSI) was developed as a research and learning tool. Full scale measurements were performed on the research vessel Polarstern during an expedition to the Arctic. This is the first comprehensive data set including vibration responses and environmental parameters to span the entire operational profile of a research voyage to the Arctic. System identification successfully identified seven global modes in the bandwidth 2 - 10 Hz. Comparisons between different methods were used to cross validate results. A modal tracking algorithm was developed and relationships between identified modes and system inputs were observed. A novel method is developed to improve the uncertainty and sensitivity of system identification and tracking, based on a data driven statistical model and a Kalman filter. A key objective is to make experimental data maximally informative by using additional system inputs. The model was found to accurately re-create the training data set and was used to make predictions based on future system inputs. The Kalman filter estimates were observed to produce balanced and consistent results. These results demonstrate the potential of an ice force estimation and structural health monitoring system.
Vibration response of the polar supply and research vessel the S. A. Agulhas II in Antarctica and the Southern ocean
(Stellenbosch : Stellenbosch University, 2014-12) Soal, Keith Ian; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Department of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Full scale measurements were conducted on the polar supply and research vessel the S.A. Agulhas II during a 78 day voyage from Cape Town to Antarctica in 2013/2014. Investigations were conducted into the effect of vibration on human comfort and the structural dynamic response of the vessel. Vibration measured in the bridge of the vessel is found to have little effect on human comfort for a standing person and is classified as not uncomfortable according to BS ISO 2631-1. Structural fatigue as a result of vibration is found to reach levels where damage is possible in the stern and where damage is probable in the bow during open water navigation, according to ship vibration guidelines by Germanischer Lloyd. Multivariate statistical analyses are performed to investigate the relationships between multiple predictor variables and vibration response. Factor analysis revealed data structure from which specific physical phenomena could be identified. Multivariable linear regression models are developed to predict vibration response and are found to provide more accurate predictions in open water than in ice. The 2-node, 3-node and 4-node normal bending modes of the structure are identified using operational modal analysis while the vessel was moored in the harbour. The natural frequencies, damping ratios and mode shapes are estimated and compared using LMS Operational PolyMAX and ARTeMIS CCSSI. A comparison of operational modal analysis results to the STX Finland finite element model show that the vessel’s modes occur at lower frequencies than numerically predicted. Clear potential is identified to further investigate structural vibration and operational modal analysis algorithm development in future research.
Whole- body vibration of heavy mobile equipment operators at an open cast mine.
(Stellenbosch : Stellenbosch University, 2017-12) Purcell, Etienne; Bekker, Annie; Muiyser, Jacques; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: The measurement and analysis of whole-body vibration was done in accordance with ISO 2631-1 at a South African opencast mine to identify potentially unhealthy levels of vibration present in vehicles. Impulsive whole-body vibration was found on all measured vehicles and 90.6% of test cases showed possibly unhealthy levels of vibration exposure. The impulsiveness of the vibration led to the underestimation of the exposure by the RMS method. Bulldozer operators were exposed to the highest average levels of whole-body vibration. It is strongly advised that the use of high exposure vehicles are limited and that job rotation is implemented to limit the vibration exposure of these individuals. The vehicle tasks are used for as well as operating conditions were found to have a significant impact on whole-body vibration. A suitable measurement duration for different types of vehicles were statistically identified and it was found that measurement durations greater than 30 min and 60 min are sufficient to measure whole-body vibration with measurement errors of less than 25% (sufficient accuracy) and 12.5% (preferable accuracy) respectively.
Whole-body vibration comfort measurement aboard the S. A. Agulhas II and just noticeable difference threshold testing in the laboratory
(Stellenbosch : Stellenbosch University, 2014-12) McMahon, Kim J.; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Department of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: A continuous comfort analysis of the whole-body vibration level aboard the S.A. Agulhas II during the 2013-2014 Antarctic voyage was conducted ac- cording BS ISO 2631-1:1997, assuming a standing posture. Just noticeable difference in magnitude testing was conducted on nine subject in the standing posture on a man-rated shaker in the laboratory environment. Two stimuli, a 5 Hz sinusoidal stimulus with a magnitude of 0,5 m.s-2 and a slamming event recoded during the voyage with a magnitude of 0,2 m.s-2 where selected as the stimuli on which to investigate the just noticeable difference thresh-old. The study shows that the vibration level for the duration of the voyage can be considered to be not uncomfortable. The results of the just notice-able difference threshold obtained for the sinusoidal stimulus concur with that found in literature for seated subjects. The just noticeable difference threshold obtained for the ship stimulus does not correlate with the results for the sinu-soidal vibration, implying that there may be an error in the vertical weighting filter provided by the standard or that Webers law does not hold for the just noticeable difference threshold of standing subjects.

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